The present invention relates to a novel foam-forming fire extinguishing composition that does not freeze at temperatures below 1.degree. C. The novel fire extinguishing composition of the present invention is useful in regions where the temperature is below 1.degree. C., such as in Alaska, the northern regions of Canada, Siberia or in the winter where extreme cold may persist and where foam-forming fire extinguishing agents are the fire extinguishing agents of choice.
In the fire extinguishing art, fires are divided into four general classes; namely, Class A, Class B, Class C and Class D.
Class A fires are those involving ordinary combustible material such as paper, wood, etc. and can be extinguished by quenching and cooling with large quantities of water or solutions containing water.
Class B fires are those involving flammable liquids fuels, gasoline, and other hydrocarbons and are difficult to extinguish. Most flammable liquids exhibit high vapor pressure along with low fire and flash points. This typically result in a wide flammability range. In this type of fire, the use of water as the sole extinguishing agent is generally ineffective because the only means of extinguishing the fire with water is through cooling.
Class C fires involve electrical equipment. Thus, the electrical conducting property of the extinguishing material is an important consideration. For this reason, it has been found that dry fire extinguishing agents are generally more useful. It has also been found that the fire extinguishing agents useful for Class A or B fires are generally also useful for Class C fires.
Class D fires involve combustible metals and are extinguished with special dry powders.
Many different fire extinguishing compositions and fire extinguishing systems using such compositions have been developed and are available on the market. However, the ability to extinguish Class A and/or Class B fires in all weather conditions and in remote regions of the globe where the temperature year round is low, remains a serious problem. The potential for a catastrophic fire in these areas is widely recognized by insurers and insured alike. Extinguishing agents and delivery systems for the protection of high value off-road mining equipment in freezing climates is of particular concern. Regularly the fire protection systems installed on this mining equipment are located on the periphery of the machine, fully exposed to the elements. Under these conditions it is necessary to have an agent that can withstand freezing temperatures for extended periods of time.
Two types of fire extinguishing agents have been developed for Class A and/or B fires: dry chemical compositions and aqueous film-forming foam (AFFF) compositions. Dry chemicals, because they are solids, are capable of use at temperatures to -40.degree. C. or -54.degree. C. depending only on the expellant gas used for discharge. The effectiveness of dry chemicals in extinguishing fires is well known. However, dry chemicals do not provide a means of blanketing the fuel surface to prevent reflash. Film-forming-foam compositions are preferred because foam formation provides a blanket to cover the fuel surface excluding air preventing further ignition of the fuel. For this reason film-forming foam compositions are particularly desirable for extinguishing fires involving flammable fuels, such as gasoline, naphtha, diesel oils, hydraulic fluids and other hydrocarbons.
Fletcher et al, U.S. Pat. No. 3,661,776, provided a 6% concentrate composition comprising a mixture of a fluoro-aliphatic carboxylic acid and a fluorinated sulphonic acids salts as the foam forming agents together with a polyoxyethylene oxide polymer, ethylene glycol and water. Chiesa, U.S. Pat. No. 3,849,315, described a composition using a mixture of lipophilic silicon containing surfactants and fluorinated hydrocarbon compounds as film forming agents. The agents are prepared as concentrated solutions and diluted with water prior to being employed to extinguish fires. These compositions contain fluorinated compounds, also known as perfluroalkyl surfactants referred to as AFFF or ARAFFF. These compositions are used as aqueous concentrates and are diluted with water when applied to a fire. Norman et al, U.S. Pat. No. 4,999,119, further described AFFF or ARAFFF in a mixture with glycols, chelating agents, pH buffers, corrosion inhibitors in water.
Other foam forming agents have been described for use in fire extinguishing compositions. Kleiner et al., U.S. Pat. No. 4,439,329, disclosed sulfide terminated oligomers, wherein the oligomers are made up of hydrophilic acrylamide copolymerized with hydrophobic and hydrophilic monomer units to generate fire extinguishing foaming compositions.
Cundasawmy et al, U.S. Pat. No. 4,770,794 further disclosed a foam forming fire extinguishing composition suitable for forest fires. The composition comprised a salt derivative of a linear alcohol as a surfactant, an alkanolamide or a polyssacharide gum or synthetic polymer as a foam stabilizer, a polyhydric alcohol ether such as ethylene glycol as a foam booster and water.
One major disadvantage of the foam-forming fire extinguishing compositions is that these compositions require dilution with water to produce the desired extinguishing effect. Dilution with water causes the composition to freeze when stored at temperatures 1 or 2 degrees below the freezing point of water. This means that the solutions must be stored in temperature controlled facilities and that prolonged application of these compositions must be at temperatures above freezing. In many parts of the world, the temperatures in the winter months are often below 1.degree. C. Moreover, the storage of the fire extinguishing compositions in heated or enclosed areas is often not possible.
An improved liquid fire extinguishing composition is, therefore, desired for use in locations where the temperature is below the freezing point. This is particularly useful for expensive mining equipment and airports located in regions of extreme cold.
It is known that mixtures of alkylene glycol, preferably ethylene or propylene glycol, can be used to depress the freezing point of water. It is also known that 50% by weight solution of either ethylene glycol or propylene glycol will lower the freezing point of water to below -40.degree. C. Such solutions are widely used as "antifreeze" in automobile cooling systems and as "de-icers" for aircraft. However, it is also known that solutions containing such a high weight percent of glycols are flammable and would not be considered desirable for use in a fire extinguishing composition.
It is also known that highly concentrated solutions of potassium acetate depresses the freezing point of the solution. To depress the freezing point by 75.degree. C. requires a solution containing 60% of potassium acetate. Typically, a solution of this concentration would be used in the aviation industry as a runway de-icer. It is also known that potassium acetate is completely biodegradable. However, it is not known to combine potassium acetate with a glycol to reduce the freezing point of an aqueous solution without having to use a high concentration of glycol which is flammable.